`@SerialComment` annotation

What is your use-case and why do you need this feature?

@SerialComment annotation will be useful for automatically generated configuration files. Some serialization libraries already implemented that feature including:

• akuleshov7/ktoml
• charleskorn/kaml
• Him188/yamlkt

And it’s possible to add comment support in other libraries like:

• kotlinx.serialization.properties
• kotlinx.serialization.hocon
• adamko-dev/json5-kotlin

The problem is that they are using/will use different @Comment annotations

Describe the solution you’d like

• Add @SerialComment annotation
• SerialDescriptor.getElementComment(index: Int): String function to get property comment SerialFormat.supportsComments property to check if SerialFormat supports comment serialization (false by default)

[sgammon]

i wonder, though, if it is possible to do make this happen without a dedicated annotation. does the compiler plugin support comments? could it just take the native Kotlin comment from the property?

[vnermolaev]

@slava110, I guess you can already achieve the goal as follows

@SerialInfo
@Target(AnnotationTarget.PROPERTY)
annotation class SerialComment(val comment: String)

fun SerialDescriptor.getElementComment(index: Int): String =
  getElementAnnotations(index)
      .filterIsInstance<SerialComment>()
      .singleOrNull()
      ?.comment
      ?: ""

@Serializable
data class Container(
    @SerialComment("Property is used for demonstration")
    val i: Int
)

fun main(args: Array<String>) {
    println(Container.serializer().descriptor.getElementComment(0))
}